1. Field of the Invention
The present invention relates to a device for generating or detecting electromagnetic radiation, such as terahertz (THz) electromagnetic radiation, and a use and fabrication method for such a device. In this specification, the terminology “the terahertz (THz) electromagnetic radiation” or “terahertz (THz) radiation” or “terahertz (THz)” is used for electromagnetic radiation in a frequency range between about 30 GHz and about 30 THz.
2. Description of the Related Background Art
In recent years, non-destructive sensing techniques have been developed using terahertz (THz) radiation. As applications of electromagnetic radiation in the above frequency range, there have been developed imaging techniques for achieving a perspective inspection apparatus capable of being safely used in place of an X-ray imaging apparatus, spectroscopy techniques for acquiring absorption spectrum and complex dielectric constant of a substance to inspect bonding conditions of atoms and molecules thereof, analytic techniques for analyzing biomolecules, and techniques for estimating carrier density and mobility, for example.
There conventionally have been proposed THz generating methods, such as a method of generating THz pulses by irradiating a photoconductive device with ultra-short pulsed laser light, and a method of generating THz continuous radiation at a beat frequency by mixing two laser light at different frequencies. In those methods of converting light into THz radiation, however, output power typically cannot be increased and power consumption typically cannot be decreased, since converting efficiencies are low.
Accordingly, an electromagnetic radiation generating method resembling a method of a semiconductor laser for emitting light has been researched. In this method, current is injected into a solid device having a semiconductor heterostructure, and electromagnetic radiation is directly generated. “Applied Physics Letters, vol. 84, p. 2494, 2004” discloses a long-wavelength laser that employs induced emission due to carrier population inversion between subbands in the conduction band. In this laser, a plurality of quantum well structures having gains are layered to increase gain. The laser is called a quantum cascade laser. Further, this semiconductor device is a laser of an edge emission type, and uses a metallic plasmon waveguide.
Further, Japanese Patent Application Laid-Open No. 8(1996)-116074 (Japanese reference) discloses a small-sized face emission structure in which a cavity using a negative resistance device is formed perpendicularly to a substrate.
However, the device of the above Japanese reference employs a semiconductor substrate with an active layer as the cavity, so that the length of the cavity cannot be flexibly regulated. Further, since its oscillation wavelength is relatively long, loss in the semiconductor substrate is relatively large, and a ratio of its gain region relative to the cavity length is small. Therefore, it is not easy to reduce its oscillation threshold.